Now let’s look at the big picture of where we are with the motor, and what needs to happen. We have it all apart and documented, ready to begin restoration. So let’s go!
There is not an exact order, but any time is great to clean and polish the metal hardware (screwheads, brackets, crankshaft – carefully!!), and get it out of the way. For heavy greasy grime use a rag soaked in solvent (e.g. mineral spirits). Rinse or wipe off and then polish with a nice product like Flitz or Autosol. Nice improvement!
Again, if ever you find the hardware heavily corroded, then replating or even replacement may be necessary. Depending on your location, someone who is very good (and reasonably priced) at metal plating can be hard to find, something to keep in mind!
Apart from the cosmetics, the major items on the checklist are to rebush necessary bearing points (will post on this soon), as the motor will get a constant workout. Then it is all about recovering and air sealing. The motor must be tight else the music begin to turn with a loping, queer motion, causing the music to lurch and stutter unpleasantly.
In order to be robust overall, this means the bellows, the slide valves and the trunk interior must all be tight individually.
Pneumatic recovery is a specialized topic which will be needed throughout the restoration process, so I will cover that separately in the next post.
The slide valves are basically just miniature wooden frames, covered on one side with motor cloth. Like a pneumatic, the cloth side must be well sealed. However just as important is a good seal between the trunk face and the inside of the valves. This is why both the valves and the trunk face must be lapped (a specific sort of sanding) completely and evenly smooth, so that they are well-mated to interface with each other.
The preferred way of doing this, traditionally, is to adhere a piece of sandpaper to a solid, dead flat surface, such as a piece of plate glass or machined table (e.g. table saw). This ensures the lapping will give the desired result. Use a medium machinist’s square (6-12″ long) to sight across the valve surface of the trunk face. Depending on how much warpage or gap you see, you will need to lap accordingly. If there are significant gaps (more than a couple of mm), you will have to either begin with a rough grade of paper (e.g. 80 grit). Work your way up to medium (120-180). If there are only light distortions in the surface, then you can proceed immediately with a fine grit (250-320) to just even it out, and that should suffice.
Incidentally, there is a detailed video of this process by (guess who?) John Tuttle. It’s a longer one, but worth checking out here.
We then finish up with a nice graphite lubrication, making sure not to mix it too light (or too heavy!) or put it on too excessively. Also, for valves like this which are in perpetual motion, don’t EVER use a greasy or “wet” lubricant for this application. This will eventually cause binding and performance issues. There might even be a warning sign about this from the original maker!
The interior of the trunk should be proofed for leakage too; it needs protection from all leaks within and without!
Now here we would normally use a heavy shellac; the traditional choice for sealing internal channels. I am instead going to use a “modern” substance. This sealer, trade name “Phenoseal”, is a little like a thinned white glue. It has a water-like consistency when applied, and then sets up (but does not ever cure 100%) like a clear plastic membrane.
I would only agree to use this under certain circumstances: it is a significant time-saver, it does as good (or better) a job than shellac, it doesn’t cause other problems, in exchange for this convenience.
Given this criteria, It is vital that this type of product is never applied to a surface which needs to be glued or which contacts a moving part, and it is never used on a surface which will have to be refinished/resurfaced in the foreseeable future.
This is why we don’t ever, EVER, use a white or yellow glue for adhering parts which may need to come apart again someday. It is a bastard of a job getting these parts apart, unless hide glue has been used. Modern glues have many wonderful uses, but should only be used in permanent structural repairs to woodworking – that’s it!
So, we have covered prepping, lapping and sealing; I will discuss recovering separately. We also need to talk about rebushing, but as mentioned that will be a separate post as well.
Once the recovering, gluing and rebushing is done, your hardware is all clean and polished, you are ready for reassembly, then regulation!
See you on the other side!